This invention relates generally to semiconductor laser devices and more particularly to semiconductor laser devices operating at wavelengths less than 700 nanometers having relatively low threshold current values and improved carrier confinement capabilities.
Semiconductor laser devices are currently utilized for a variety of applications. In particular visible light laser diodes may be used for pumping of solid state lasers whose absorption spectra are in the visible wavelength range, optical recording, high definition television, medical devices and transmission through plastic optical fibers. Visible light diode lasers operating in the 630 to 680 nanometer wavelength range and utilizing GaInP/AlGaInP materials systems, however, have relatively high threshold current densities primarily due to poor carrier confinement.
A graded index separate confinement heterostructure (GRINSCH) structure has been reported by Bour and Shealy in Applied Physics Letters, Volume 51, (21), pages 1658-1660 in 1987 in an article entitled High Power (1.4 W) AlGaInP Graded-Index Separate Confinement Heterostructure (.lambda.=658nm)Laser. The GRINSCH structure was an attempt to reduce the threshold current density of GaIn P/AlGaInP visible light diode lasers. Additionally, it has been reported in Electronics Letters, Volume 26, page 1375 in 1990 in an article by Katsuyama, et al. entitled Very Low Threshold Current AlGaInP/GaInP strained Single Quantum Well Visible Diode Laser that the use of a strained active layer or a strained quantum well rather than a lattice matched quantum well tends to decrease the threshold current density as well. However, in the GaInP/AlGaInP diode laser utilized by Katsuyama, et al. the strained layer quantum well was positioned between a pair of step index confinement layers and not a GRINSCH structure. While both of these approaches, graded index confinement layers and strained active layers when utilized individually have been partially successful in decreasing the threshold current density of a GaInP/AlGaInP diode laser, the confinement is still desired to be improved and thus the threshold current density decreased in order to have more efficiently operating visible light diode lasers.
In an article entitled InGaAs/AlGaAs Strained Single Quantum Well Diode Lasers with Extremely Low Threshold Current Density and High Efficiency in Applied Physics Letters, Volume 57 (4), page 231 in 1990, Choi and Wang utilized bounding layers positioned about a quantum well in order to decrease the threshold current density of a semiconductor laser. Choi and Wang utilized a semiconductor laser comprised of InGaAs/AlGaAs which produces significantly longer wavelengths than a visible light diode laser comprised of GaInP/AlGaInP materials.
Therefore, it would be desirable for a semiconductor laser diode emitting visible light particularly in the spectra of 630 to 680 nanometers and comprised of GaInP/AlGaInP material systems to have improved carrier confinement and thus a relatively low threshold current density so as to more efficiently produce the visible light output.